Generally, intoxicated drivers are a major cause of traffic accident fatalities in the United States. A recent National Highway Traffic Safety Administration (NHTSA) report showed that 40% of the total accident fatalities in the U.S. in the year 2003 were alcohol related. More specifically, 12,373 motor vehicle occupants were killed in crashes that involved a blood alcohol concentration (BAC) of 0.08 g/dL or higher. This equates to over 33% of the 37,132 U.S. motor vehicle fatalities in 2003. In addition to the societal impact, the cost of such crashes in the U.S. is about $40 billion per year. It is well established that the rate of fatal traffic accidents per mile traveled is related to a driver's BAC and that there is a correlation between impairment in driving skills and the driver's BAC. The definition of drunk driving in the U.S. involves a BAC level of 0.08 g/dL. A primary countermeasure to combat drunk driving in the U.S. is the criminal justice system, which employs deterrents and sanctions against drunk drivers. Various other approaches to combat drunk driving have been utilized.
One existing approach to combat drunk driving utilizes an electrochemical sensor that measures ethanol concentration in air. Generally, ethanol concentration in human breath is a good indication of BAC. Inside the air sacs in the human lung, there is a chemical equilibrium between the concentration of ethanol in the air and the concentration of ethanol in an individual's blood. For law enforcement purposes, an electrochemical sensor can be built into an object such as a clipboard or flashlight that a police officer can, under certain circumstances, justifiably insert into a vehicle. Electrochemical sensors can also be used in commercially available interlocks, which can be mandated following a driver's drunk driving conviction. However, currently available electrochemical sensors typically have a limited lifetime and typically must be replaced after about three years. Generally, to be used as an on-board component of the safety system, an ethanol sensor must have a lifetime of at least ten to fifteen years. Another electrochemical sensor that can be used includes a device that is pressed against an individual's skin to determine alcohol intoxication through remote detection of ethanol that evaporates from the driver's skin. Other approaches typically involve passing infrared through the driver's extremities, such as a finger, or using Raman spectroscopy to measure the concentration of ethanol in the fluid at the surface of the driver's eyes. Generally, these approaches are impractical for on-board vehicle use as well.
Another approach to combat drunk driving uses a heated film of metal oxide that changes electrical resistance in response to ethanol concentration. Such sensors are sometimes used in handheld devices sold to consumers, typically to self test their BAC. However, such sensors generally operate with undiluted breath from the driver. The breath sample is undiluted and so the detection level needed is only about 210 parts per million (ppm) of ethanol, by volume. Also, the minimum ethanol concentration that can be reliably detected with a metal oxide film is typically in the range of 10 to 50 ppm.